[ConstraintElim] Enable pass by default.

The pass should help to close a functional gap when it comes to
reasoning about related conditions in a relatively general way.

It addresses multiple existing issues (linked below) and the need for a
more powerful reasoning system was also discussed recently in
https://discourse.llvm.org/t/rfc-alternative-approach-of-dealing-with-implications-from-comparisons-through-pos-analysis/65601/7

On AArch64, the new pass performs ~2000 simplifications on
MultiSource,SPEC2006,SPEC2017 with -O3.

Compile-time impact:

NewPM-O3: +0.20%
NewPM-ReleaseThinLTO: +0.32%
NewPM-ReleaseLTO-g: +0.28%

https://llvm-compile-time-tracker.com/compare.php?from=f01a3a893c147c1594b9a3fbd817456b209dabbf&to=577688758ef64fb044215ec3e497ea901bb2db28&stat=instructions:u

Fixes #49344.
Fixes #47888.
Fixes #48253.
Fixes #49229.
Fixes #58074.

Reviewed By: asbirlea

Differential Revision: https://reviews.llvm.org/D135915